A commonly used bookbinding system is seen in U.S. Pat. No. 4,369,013 issued Jan. 18, 1983 to Messrs. Abildgaard and Groswith (Reissued as Bl 4,369,013 June 14, 1988) and sold as the VeloBind.RTM. system. This system uses elongated plastic strips, one strip having integral studs equally spaced along the strip and fitting through the holes in punched paper and the second strip having round apertures matching the studs, which other strip is placed over the ends of the studs emerging from the paper stack. Upon cinching the strips together to compress a marginal edge of the paper sheets stack, the excess length of the studs are cut off and riveted into recesses formed in the second strip.
In accord with another VeloBind invention seen in U.S. Pat. No. 4,620,724 issued Nov. 4, 1986, the round studs of the '013 design may also be employed for binding a paper sheets stack having punched rectangular holes. In the '724 patent a particular spacing of two studs at one end of the strip is provided so as to prevent lateral displacement of the punch paper in the stack.
While the VeloBind '013 system results in a tight permanent bind which is satisfactory in normal use, it has been found that when a book so bound is dropped or otherwise subjected to an impact, particularly at the end of the strips as shown in FIG. 1, the end riveted studs tend to pop, either by breakage at the root of the stud or extrusion of the plastic rivet head back out of the matching second strip aperture. Impact forces, as seen in FIG. 2, tend to splay out the bound sheets at the strip bottom corner and this action moves the strip ends outwardly as seen in FIG. 3 with the result that the stud is sheared from the strip at its root, and/or due to the resultant tension forces a rear extrusion of the plastic rivet head from the binding, both as seen in FIG. 4. The result of this stud breaking action is the unaesthetic loss of binding symmetry, a loose bottom binding edge, breach of the binding integrity and the resultant unattractive stacking of various bound books or reports.